The instant invention deals with land transportation means in which such means operates over relatively short stretches between one stop and the following one. In particular, this invention deals with mass transportation systems, such as the urban transportation systems, where many intermediate stops at determined places must be effected. Considering, by way of example, urban transportation means, which practically have not been subjected to changes in the last half century, it is possible to distinguish: transportation means having a rigidly constrained path, which derive from the urbanized railway, such as trams (trolley-cars), underground vehicles, monorail vehicles, and like; transportation means having a free path, such as motorbuses; and transportation means having a semi-constrained path, such as trolley-buses.
Of these transportation means, the tram is declining in usage by reason of its rigidly constrained path which makes it unable to overcome any hindrance on its way, missing the agility and flexibility which is required in the modern traffic. The motorbus, which is mainly diesel motor powdered, is the most common and widespread transportation means by reason of its path freedom. However, its propulsive system has a serious disadvantage: air pollution caused by exhaust gases of internal combustion engines. In addition, the pollution is increased by the fact that during the service the engine remains in operation even at the stops. Other disadvantages are the wasting of energy due to the low efficiency of the engine and its noise. The trolley-bus, being free from rail constraints, thus not having a rigidly constrained path, was expected to replace trolley cars as well as motorbuses. In fact, it has the non-polluting, noiseless, and nimbleness advantages of electric traction. In spite of these advantages, use of the trolley bus has not spread as expected due to other disadvantages, such as: cost and complexity in building up the two pole electrical aerial power line; very high maintenance cost of the aerial lines; the impossibility for the vehicle to deviate to paths which are not provided with electrical power lines; and the limited transverse freedom allowed by the trolley, which is subject to disjunction from the line, if the trolley-bus, in order to avoid encumbrances, deviates transversely too much will respect to the electrical line.
As a consequence, actual research projects are devoted to the development of urban transportation means free fron any path constraint (power lines) or rigid way constraint (rails), as it is for the motorbus, and, however, noise and pollution exempt as it is for electrically powered vehicles. Many solutions have been proposed and many attempts made without obtaining a satisfactory result. Storage battery powered vehicles have been developed which are believed to be the best way to solve the problems of urban traffic. At the present day, however, they are not used because the energy sources available have a serious limitation: the very low value of specific energy stored per weight unit as compared to that for commonly used fuels. It may be verified that given the same useful energy, that is at equal vehicle performance, the ratio between storage battery weight and fuel weight is about 100, at the actual state of the art. It is estimated that this will be lowered to about 20 in the next years, if research projects presently under way will provide the expected results. In other words, the useful energy (convertible to kinetic energy) obtained, for instance, from 120 liters of diesel oil, whose weight is about 100 kilograms (this may be assumed as a standard quantity for a motorbus), would require today 10,000 kilograms of storage batteries and presumably 2,000 kilograms in the future.
An approach to reduce this weight, which is prohibitive for the operation of an electrical vehicle (apart from the cost), is the one presently on study by German manufacturers: by reducing the range to a safe minimum (a small fraction of the one provided by combustion vehicles) the weight and the cost of the batteries is reduced. The batteries, however, must be replaced in a suitable station provided with a fast loading/unloading facility and a station network must be provided for that purpose. This solution has the following drawbacks: the need to stop the service rather frequently, said each hour as a minimum, for an interval of five minutes (so the designers say), in order to replace the batteries; the need to establish a station network in order to replace the batteries quickly; recharging apparatus at each station; and large capacity required for each vehicle, considering the recharging time of a battery volume equal to that necessary for a range of 1 day. On this subject, information may be found in the article "German Electric Prototype Vehicle Features Fast `Refuel` Stops" in Product Engineering, May 1971, Page 23.
Another approach, aiming to provide an ideal urban transportation system, has been followed unsuccessfully by the Swiss firm OERLINKON in the fifties: apparently the vehicle was a trolley-bus, since it was provided with a trolley, but the electrical power line was not needed. The concept followed was to produce the electric power required for traction by conversion through a generator of the kinetic energy stored in a flywheel, which energy in turn, was taken by conversion, through a motor, of the electric energy supplied through the trolley during stops at prefixed stations. Such a vehicle has never been placed in public use by reason of many inconveniences: the low value of the storable specific energy and consequently limited range (about 1 kilometer for a vehicle of weight and performances equivalent to those of a trolley-bus); a recharging time for the flywheel which is too long; the dynamic accumulation of energy and, therefore, storage limited in time and the energy decreasing by reason of friction even when unused; the complexity of the flywheel clutch and the controls for the motor-generator-flywheel; and serious interference with the movement and driving of the vehicle due to the gyroscopic precession torque produced by the flywheel during changes in vehicle direction. Recently the same idea has been reconsidered by a well known American aerospace company which, by means of many technological improvements aims to increase the specific energy stored in the flywheel so as to obtain a greater range. The proposed vehicles would operate as a common trolley-bus for a certain portion of their way, draining energy from the electrical line for their movement as well as for charging the flywheel. Then they will continue for the remainder of the way using the energy stored in the flywheel. (See Product Engineering, July 20, 1970, pp. 80 and Apr. 12, 1971, pp. 54).